igneous
Water-worn dark beach pebble
Likely fine-grained basalt or dolerite (diabase)
AI-generated identification · may be incorrectDark gray-brown, rounded and smoothed by abrasion, with a dull to faintly satin luster and very fine granular texture. Typical hardness is about Mohs 6–7; massive, non-cleaving, and relatively dense (specific gravity ~2.8–3.1).
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Physical properties
Dark gray-brown, rounded and smoothed by abrasion, with a dull to faintly satin luster and very fine granular texture. Typical hardness is about Mohs 6–7; massive, non-cleaving, and relatively dense (specific gravity ~2.8–3.1).
Formation & geological history
Likely an eroded volcanic rock transported and polished by waves; basalt formed from rapidly cooled lava, whereas dolerite crystallized at shallow depth. Its exact geological age cannot be determined from the photograph.
Uses & applications
Common basalt is used for aggregate, roadstone, riprap, and paving; attractive pebbles are used in landscaping, crafts, and inexpensive specimen collections rather than fine jewelry.
Geological facts
The smooth surface and rounded edges indicate prolonged water abrasion, not natural crystal growth. A fresh fracture would typically reveal a dark, fine-grained interior, sometimes with tiny feldspar crystals or vesicles.
Field identification & locations
Common in coastal and river gravels worldwide, especially near volcanic terrains. Check for magnetism, a pale-gray streak, absence of visible quartz, and resistance to scratching by a steel file; photo-based identification is provisional.
